1. Field of the Invention
This invention belongs to the fields of pharmaceutical and synthetic organic chemistry, and provides an improved process for preparing novel intermediates in the synthesis of anti-viral benzimidazoles. The intermediates are sulfonated o-phenylenediamines, and carry a trans-.alpha.-alkylidenebenzyl group at the 5-position.
2. State of the Art
The Benzimidazoles which are the ultimate products of the present process are taught by Paget, U.S. Pat. No. 4,118,742. The patent teaches a number of processes for the preparation of the benzimidazoles; its general process is to form the benzimidazole with the 1-position unsubstituted, and sulfonate as a final step.
The patent does not distinguish between the isomeric .alpha.-alkylidenebenzyl substituents of its compounds. See examples 72 and 74 of the patent, which do not discuss the isomeric form of the alkylidenyl substituents. It has since been discovered that the trans form of the alkylidenyl substituent is preferable, and the present process selectively forms the trans isomers. Neither does the patent suggest that the imidazole ring could as the final step, after the sulfonylamino and alkylidene groups had been selectively formed. U.S. Patent Application Ser. Nos. 373,944 and 373,945, of Ryan and Slomski, and of Dominianni, teach processes for preparing the starting compounds of the present process.